Quick couplings in general are common devices for coupling fluid lines, without the need for special tools. Quick couplings, for example, may be configured as individual couplings for the connection of a single fluid line. Individual quick couplings typically have a ball locking mechanism to hold two halves of the coupling together as they try to separate from internal pressures. In common usages, individual quick couplings may be employed to connect sections of a hydraulic fluid line, and the ball locking mechanism operates to prevent separation under the hydraulic pressure.
Alternatively, a quick coupling may be configured as a multi-coupling for connecting any number of multiple fluid lines. The multi-coupling constitutes a group of quick couplings mounted together in a plate or casting. In place of an individual locking mechanism for each individual coupling, a multi-coupling typically has a larger centralized locking mechanism that connects and holds the group of couplings together. The mechanical advantage of this single locking mechanism is often needed to overcome the combined forces required to connect all of the quick couplings simultaneously. A centralized locking mechanism may be employed singularly or in combination with one or more satellite locking mechanisms that supplement the operation of the centralized locking mechanism. There are many industry common locking mechanisms for multi-couplings, including, for example, cam locking mechanisms and screw locking mechanisms as are known in the art.
Multi-couplings may be employed for connecting high pressure fluid lines, often under extreme conditions. For example, multi-couplings are employed for connecting multiple fluid lines associated with offshore and subsea operations. Such multi-couplings may connect fluid lines between the equipment itself and the related control systems. One half of the multi-coupling typically is a fixed plate that is attached to base equipment on the control system side of the system. The other half of the multi-coupling is a free plate that initially is moveable into position for coupling relative to the fixed plate. A locking mechanism as referenced above is then employed to connect the plates. Screw locking mechanisms are commonly used in multi-couplings in deep water operations. The locking mechanism typically includes a drive mechanism for forcing the free plate to join with the fixed plate in a locked configuration.
In deep sea operations, the combination of salt water, high pressures, and other adverse local conditions results in a highly corrosive environment. Accordingly, the materials of the multi-coupling, and particularly the threading joints of the screw locking mechanisms, are selected in part so as to be corrosion resistant. High nickel content metal alloys have proven suitable to resist corrosion under such conditions. Such nickel-based materials, however, also have a high risk of galling as between threaded components of the locking mechanism. As is known the art, “galling” is process by which under high pressures, a friction-based weld undesirably occurs between two sliding surfaces. Galling is particularly common for threaded fastening elements in high pressure environments, and results in the male and female threads being completely welded together rendering the threads useless.
Conventional multi-couplings with a screw-type locking mechanism are useless once galling occurs, because the plates of the multi-coupling cannot be disconnected and re-connected. In the context of deep sea operations, galling generates friction-based welds between the locking mechanism components that join the free plate and the fixed plate of the multi-coupling structure. A galled locking mechanism conventionally must be cut out from the plates, which can ruin the plates and otherwise complicates servicing and maintaining the multi-coupling. In addition, replacing galled locking mechanisms in conventional configurations, if it can be done at all, typically requires that the fixed plate be removed from its base equipment, which is difficult and time consuming.